optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code

optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code

[reichelt]

>Number:         6189
>Category:       optimization
>Synopsis:       Regression from 3.0.x: g++ -O3 generates wrong code
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Apr 05 07:56:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Volker Reichelt
>Release:        gcc version 3.1 20020325 (prerelease)
>Organization:
>Environment:
i686-pc-linux-gnu, mips-sgi-irix6.5
>Description:
The following small C++-program should return 1,
but compiling the code with "g++ -O3" I get 0 as a result.

----------------------------snip here---------------------
class A
{
  private:
    int x[2];

  public:
    int& GetFirst() { return x[0]; }
};


A foo ()
{ 
    A a;
    a.GetFirst()=1;
    return a;
}


int main()
{
    A b=foo();
    return b.GetFirst();
}
----------------------------snip here---------------------

With less optimization the problem disappears.
It even disappears when I replace "private" by "public".

The bug is a regression from gcc 3.0.x.
>How-To-Repeat:
g++ -O3 bug.cpp; a.out; echo $?
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code

[reichelt]

Synopsis: Regression from 3.0.x: g++ -O3 generates wrong code

State-Changed-From-To: open->closed
State-Changed-By: reichelt
State-Changed-When: Mon Oct 28 13:22:20 2002
State-Changed-Why:
    Fixed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6189

Re: optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code

[Jason Merrill]

The following reply was made to PR optimization/6189; it has been noted by GNATS.

From: Jason Merrill <jason@redhat.com>
To: Reichelt <reichelt@igpm.rwth-aachen.de>
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: optimization/6189: Regression from 3.0.x: g++ -O3 generates
 wrong code
Date: Mon, 10 Jun 2002 15:06:07 +0100

 >>>>> "Reichelt" == Reichelt  <reichelt@igpm.rwth-aachen.de> writes:
 
 > Is there any reason why you did not close the PR? The problem seems to
 > be fixed in gcc 3.1 as well as in mainline (gcc 3.2 20020610).
 
 Because I thought we might want to fix it in a hypothetical 3.0.5 release.
 
 Jason

Re: optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code

[Reichelt]

The following reply was made to PR optimization/6189; it has been noted by GNATS.

From: Reichelt <reichelt@igpm.rwth-aachen.de>
To: jason@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: optimization/6189: Regression from 3.0.x: g++ -O3 generates wrong code
Date: Mon, 10 Jun 2002 15:25:24 +0200

 Hi Jason,
 
 thanks for fixing the bug.
 
 Is there any reason why you did not close the PR? The problem seems to
 be fixed in gcc 3.1 as well as in mainline (gcc 3.2 20020610).
 
 By the way, the link for the new testcase
   http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/nrv3.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
 doesn't work (at least not for me). However, the following works fine:
   http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/nrv3.C?rev=1.1
 Could you please update it?
 
 Greetings,
 Volker Reichelt
 
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6189